Optical information recording medium and method of producing a master and stampers therefor

ABSTRACT

New and unobvious techniques for manufacturing optical information recording media (such as a phase-change type optical disc), including techniques for producing a master and stampers for producing the optical information recording media, are provided. Exposure light beams are controlled to form information recording tracking tracks and phase pits reliably and precisely.

CROSS REFERENCE TO RELATES APPLICATIONS

This application is a continuation of co-pending application Ser. No.09/406,570, filed Sep. 24, 1999, which is a continuation-in-part (andincorporates by reference therein the entire contents) of applicationSer. No. 09/140,975, filed Aug. 27, 1998, now abandoned. The entirecontents of application Ser. Nos. 09/406,570 and 09/140,975 areincorporated by reference herein.

FIELD

This patent specification relates to an optical information recordingmedium such as a phase-change type optical disc, and to techniques forproducing a master and stampers for producing the optical informationrecording medium.

BACKGROUND

Optical recording media such as phase-change type optical recordingmedia, typically have synchronization signals and/or address or otherinformation (often called “pre-format information”) recorded as phasepits on the disc as a part of the disc manufacturing process. When thedisc is formed by injection molding using stampers made from masters,such information is recorded on the master by forming correspondingphase pits therein. Such pre-format information can be in the form of azigzag line (wobbling the groove), or can be represented by changing thelength, distance, and position of a discontinuous groove (hereinafter,such groove is called “phase pit”).

For the purpose of increasing the recording capacity of an optical disc,it is desirable to reduce the distance between the grooves employed asthe information recording track (hereinafter, such distance is called“track pitch”). However, the need for a sufficient S/N (signal to noiseratio) restricts the recording capacity of the optical informationrecording medium in the case of utilizing the wobbling method. Usingother methods can also impose limitations when recording capacity isincreased, because the need remains to ensure adequate S/N.

Japanese Laid-open Patent Application No. 9-17029/1997 proposes formingphase pit on the lands that are between the grooves that carry therecording track. FIGS. 23 a through 23 c schematically illustrate thisapproach, and show phase pits P formed on the lands L that are betweenthe recording grooves G. As illustrated in FIGS. 23 a through 23 c, thephase pits P connect in the radial direction respective adjacent grooveswhere the recording tracks are. Viewed in the track direction, a phasepit resemble a rung of a ladder. Such phase pits P can be read with aphotodiode pair arranged in the radial direction (in the directionperpendicular to the track direction) of the optical disc. The diodepair and its associated electronics receive light energy modulated bythe phase pits and process it into a differential electrical signal.Details of this process can be found in connection with FIG. 8 in thepublished specification of Japanese Laid-open Patent Application No.9-17029/1997. In this arrangement, if two phase pits P flank a groove Gat the same track position, the pre-format information that the twophase pits represent may be read at the same time to cause undesirablecross-talk.

In order to reduce cross-talk, two types of pre-format information phasepits P are formed, EVEN pattern for an even number and ODD pattern foran odd number, and those patterns are changed from one to the other in acase (such as mentioned above) in which cross-talk may occur. For moredetail, refer to FIG. 2 and the explanation corresponding to FIG. 2 inthe published specification of Japanese Laid-open Patent Application No.9-17029/1997. By adopting the above-mentioned method, cross-talk can bereduced.

However, it can be difficult to determine ahead of time the positions atwhich cross-talk can occur, that is, where phase pits P simultaneousexist on the lands L at the right and left of a groove G when exposing amaster, in order to change from one to the other of the even patternEVEN and the odd pattern ODD. If there are no errors in monitoringtracks or revolutions or determining positions along a track in themastering process, the positions at which cross-talk can occur may bedetermined by calculation and the phase pit pattern of the pre-formatinformation can be encoded by changing from one to the other of the evenpattern EVEN and the odd pattern ODD. However, an error can occur in themastering process, and even if the error is small (e.g., no larger than0.1%), cross-talk typically is not sufficiently alleviated.

In practice, an additional factor that makes it difficult to maintainaccuracy is that the length of the phase pit P in the track direction isof the order of sub-micron, and therefore it is often desirable tomonitor the rotation of the master during exposure to nanosecond (ns)accuracy.

There is a method of reading phase pit pre-format information employinga push-pull signal (difference signal), although such method is notdescribed in detail in the aforementioned published specification. Someprinciples of reading (reproducing) the pre-format information aredescribed hereinafter, referring to FIGS. 24(a), 24(b), and FIGS. 25(a),25(b).

FIG. 24(a) shows a plan view of a phase pit P. FIG. 24(b) illustratesthe waveform of a push-pull signal generated from the vicinity of thephase pit P by a reading beam B traversing the disc generally in theradius direction thereof, as illustrated in FIG. 24(a). The push-pullsignal approximates a sinusoidal wave with a period corresponding to thetrack pitch TP. Since there is asymmetry in the vicinity of the phasepit P in the radial direction relative to the track center, there is ashift related to the phase pit P (in FIGS. 24(a) and 24(b), shown by adot-and-dash line), by a distance s in the radius direction from thetrack center of the groove G.

For this reason, when controlling the tracking along the groove G andreproducing a signal as shown in FIG. 25(a), a peak represented by amagnitude A appears in the push-pull signal for the position of thephase pit P as illustrated in FIG. 25(b). If the presence or absence ofthe peak A or the location of such a peak is detected, the pre-formatinformation represented by the phase pit P can be reproduced.

However, when two phase pits P are radially adjacent, on two landsflanking the same groove G, for example at track shown in FIG. 26(a),even though the phase pits P exist, there is no radial asymmetry alongtrack Tr4. A positional shift s does not occur at the center of thephase pit, as is apparent from the push-pull signal shown in FIG. 26(b).Consequently, the peak A may not appear at all in the push-pull signalin the case of reproducing the signal by performing tracking control,along the groove G in this case. Namely, in a case in which the phasepits P exist at the same time on the lands L situated at the right andleft sides of the groove G, there arises a problem that the pre-formatinformation formed with the phase pit P cannot be detected reliably.Consequently, in order to solve the above-mentioned problem, even in thecase of reproducing with a push-pull signal, two types of patterns ofthe pre-format information formed with the phase pits P (for example,EVEN pattern for an even number and ODD pattern for an odd number) areprepared, the patterns are changed over, and one of the patterns is usedin the case of an arrangement generating the cross-talk.

Accordingly, this patent specification is directed to realizing anoptical information recording medium which is not affected by cross-talkeven when phase pits exist on the lands situated at the right and leftsides of a groove and in which the address information, etc., encoded byphase pits can be reproduced reliably.

SUMMARY

This patent disclosure provides new and unobvious techniques formanufacturing optical information recording media. One aspect of thisdisclosure includes optical information recording media capable ofreliably reproducing phase pit information, without being significantlyaffected by mutual interference of two phase pits that are radiallyadjacent to each other.

An optical information recording medium, according to one exemplaryembodiment, includes information recording tracks configured to serve asgrooves, and phase pits formed on the tracks in a way such that radiallyopposite edge portions of the phase pits orthogonal to the tracks havetilt angles different from each other, wherein preformatted informationis recorded as the phase pits.

In another exemplary embodiment, an optical information recording mediumincludes grooves configured to serve as information recording tracks,and phase pits formed on the tracks in a way such that radially oppositeedge portions of the phase pits orthogonal to the tracks have tiltangles different from each other, wherein preformatted information isrecorded as the phase pits, and wherein a track center of the groovesand a center of the phase pits are substantially identical, gap widthsof the grooves and the phase pits are substantially identical, and gapdepths of the grooves and the phase pits are substantially identical.

According to yet another exemplary embodiment, an optical informationrecording medium includes grooves configured to serve as informationrecording tracks, and phase pits formed on the tracks in a way such thatradially opposite edge portions of the phase pits orthogonal to thetracks have tilt angles different from each other, wherein preformattedinformation is recorded as the phase pits, and wherein a center of thephase pits is radially displaced relative to a track center of thegrooves, a gap width of the phase pits is greater than a gap width ofthe grooves such that each of the phase pits leaves a radial clearancefrom an immediately adjacent one of the grooves, and gap depths of thegrooves and the phase pits are substantially identical.

In yet another exemplary embodiment, an optical information recordingmedium includes grooves configured to serve as information recordingtracks, and phase pits formed on the tracks in a way such that radiallyopposite edge portions of the phase pits orthogonal to the tracks havetilt angles different from each other, wherein preformatted informationis recorded as the phase pits, and wherein a center of the phase pits isradially displaced relative to a track center of the grooves such thateach of the phase pits leaves a radial clearance from an immediatelyadjacent one of the grooves, gap widths of the grooves and the phasepits are substantially identical, and gap depths of the grooves and thephase pits are substantially identical.

Another aspect of the disclosure pertains to original medium exposingmethods for exposing a master for use in manufacturing opticalinformation recording medium.

According to one exemplary embodiment, an original medium exposingmethod for producing an optical information recording medium includesarranging a groove exposure beam at a track-center oriented position,arranging a phase pit exposure beam at a place radially displaced from atrack center, conducting a groove exposure with the groove exposurebeam, and conducting a phase pit exposure substantially simultaneouslywith the groove exposure, wherein in a time of the phase pit exposure, alight amount of the groove exposure beam is reduced, and a light amountof the phase pit exposure beam is smaller than the reduced light amountof the groove exposure beam.

In another exemplary embodiment, an original medium exposing method forproducing an optical information recording medium includes conducting agroove exposure for exposing an original medium with an exposure beam byarranging the exposure beam at a track-center oriented position,conducting a phase pit exposure for exposing the original medium withthe exposure beam which is slightly displaced in a radial direction fromthe track-center oriented position, wherein a light amount of the phasepit exposure is reduced from a light amount used in the groove exposure,wherein, in the optical information recording medium, grooves serve asinformation recording tracks and phase pits are formed as preformattedinformation on the tracks in a way such that radially opposite edgeportions of the phase pits orthogonal to the tracks have tilt anglesdifferent from each other, and wherein a center of the phase pits isradially displaced relative to a track center of the grooves, a gapwidth of the phase pits is smaller than a gap width of the grooves, andgap depths of the grooves and the phase pits are substantiallyidentical.

According to yet another exemplary embodiment, an original mediumexposing method for producing the optical information recording mediumincludes arranging a groove exposure beam at a track-center orientedposition, arranging a phase pit exposure beam at a place radiallydisplaced from a track center, conducting a groove exposure with thegroove exposure beam, and conducting a phase pit exposure substantiallysimultaneously with the groove exposure, wherein in a time of the phasepit exposure, a light amount of the groove exposure beam is reduced anda light amount of the phase pit exposure beam is smaller than thereduced light amount of the groove exposure beam.

In yet another exemplary embodiment, an original medium exposing methodfor producing the optical information recording medium includesarranging a groove exposure beam at a track-center oriented position,arranging a phase pit exposure beam at a place radially displaced from atrack center, conducting a groove exposure with the groove exposurebeam, and conducting a phase pit exposure substantially simultaneouslywith the groove exposure, wherein in a time of the phase pit exposure, alight amount of the groove exposure beam is reduced and a light amountof the phase pit exposure beam is smaller than the reduced light amountof the groove exposure beam.

An original medium exposing method for producing an optical informationrecording medium, according to another exemplary embodiment, includesconducting a groove exposure for exposing an original medium with anexposure beam by arranging the groove exposure beam at a track-centeroriented position, conducting a phase pit exposure for exposing theoriginal medium with a phase pit exposure beam which is slightlydisplaced in a radial direction from the track-center oriented position,wherein a light amount of the phase pit exposure beam is reduced from alight amount of the groove exposure beam, wherein, in the opticalinformation recording medium, grooves serve as information recordingtracks and phase pits are formed as preformatted information on thetracks in a way such that radially opposite edge portions of the phasepits orthogonal to the tracks have tilt angles different from eachother, and wherein a center of the phase pits is radially displacedrelative to a track center of the grooves, a gap width of the phase pitsis greater than a gap width of the grooves such that each of the phasepits leaves a radial clearance from an immediately adjacent one of thegrooves, and gap depths of the grooves and the phase pits aresubstantially identical.

Another aspect of the disclosure pertains to making masters and stampersfor manufacturing optical information recording media

An exposure method for exposing a master for manufacturing an opticalinformation recording medium, according to one exemplary embodiment,includes exposing a light-sensitive layer of the master, to form on thelight-sensitive layer a first latent image corresponding to a groove, byapplying an exposure beam having constant light intensity and centeredat a center of a track on the master, and shifting the exposure beam ina radial direction from the center of the track, and exposing thelight-sensitive layer with the shifted exposure beam, to form on thelight-sensitive layer a second latent image corresponding to a phasepit. The exposure method may be included in a stamper manufacturingmethod and an optical information recording medium manufacturing method.Apparatuses which apply the exposure method to manufacture masters,stampers and/or optical information recording media are also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present application can be more readily understoodfrom the following detailed description with reference to theaccompanying drawings wherein:

FIGS. 1(a) through 1(c) illustrate a portion of an optical informationrecording medium of a first embodiment, wherein FIG. 1(a) is a plan viewof the recording medium, FIG. 1(b) is a cross-sectional view taken alongline 1 and FIG. 1(c) is a cross-sectional view taken along line 2;

FIGS. 2(a) through 2(f) graphically illustrate a master and stampermanufacturing process;

FIG. 3 shows a schematic view illustrating exposure of a master;

FIGS. 4(a) through 4(c) show explanatory diagrams for illustratingexemplarily a method of exposing a master;

FIGS. 5(a) through 5(c) illustrate a portion of an optical informationrecording medium of a second embodiment, wherein FIG. 5(a) is a planview of the recording medium, FIG. 5(b) is a cross-sectional view takenalong line 1 and FIG. 5(c) is a cross-sectional view taken along line 2;

FIGS. 6(a) and 6(b) show explanatory diagrams for illustratingexemplarily a method of exposing a master;

FIG. 7 shows an explanatory diagram for illustrating exemplarily amethod of exposing a master for the third embodiment;

FIGS. 8(a) through 8(c) illustrate a portion of an optical informationrecording medium of a fourth embodiment, wherein FIG. 8(a) is a planview of the recording medium, FIG. 8(b) is a cross-sectional view takenalong line 1 and FIG. 8(c) is a cross-sectional view taken along line 2;

FIGS. 9(a) and 9(b) show explanatory diagrams for illustratingexemplarily a method of exposing a master;

FIGS. 10(a) through 10(c) illustrate a portion of an optical informationrecording medium of a fifth embodiment, wherein FIG. 10(a) is a planview of the recording medium, FIG. 10(b) is a cross-sectional view takenalong line 1 and FIG. 10(c) is a cross-sectional view taken along line2;

FIGS. 11(a) and 11(b) show explanatory diagrams for illustratingexemplarily a method of exposing a master;

FIGS. 12(a) through 12(c) illustrate a portion of an optical informationrecording medium of a sixth embodiment, wherein FIG. 12(a) is a planview of the recording medium, FIG. 12(b) is a cross-sectional view takenalong line 1 and FIG. 12(c) is a cross-sectional view taken along line2;

FIGS. 13(a) and 13(b) show explanatory diagrams for illustratingexemplarily a method of exposing a master;

FIG. 14 shows an explanatory diagram for illustrating exemplarily amethod of exposing a master for a seventh embodiment;

FIGS. 15(a) through 15(c) illustrate a portion of an optical informationrecording medium of an eighth embodiment, wherein FIG. 15(a) is a planview of the recording medium, FIG. 15(b) is a cross-sectional view takenalong line 1 and FIG. 15(c) is a cross-sectional view taken along line2;

FIG. 16 shows an explanatory diagram for illustrating exemplarily amethod of exposing a master;

FIGS. 17(a) and 17(b) illustrates a first example, wherein FIG. 17(a) isan LPP property diagram (graph) and FIG. 17(b) is an explanatory diagramfor illustrating conditions thereof;

FIGS. 18(a) and 18(b) illustrate a second example, wherein FIG. 18(a) isan LPP property diagram (graph) and FIG. 18(b) is an explanatory diagramfor illustrating conditions thereof;

FIGS. 19(a) and 19(b) illustrate a third example, wherein FIG. 19(a) isan LPP property diagram (graph) and FIG. 19(b) is an explanatory diagramfor illustrating conditions thereof;

FIGS. 20(a) and 20(b) illustrate a fourth example, wherein FIG. 20(a) isan LPP property diagram (graph) and FIG. 20(b) is an explanatory diagramfor illustrating conditions thereof;

FIGS. 21(a) and 21(b) illustrate a fifth example, wherein FIG. 21(a) isan LPP property diagram (graph) and FIG. 21(b) is an explanatory diagramfor illustrating conditions thereof;

FIGS. 22(a) and 22(b) illustrate a sixth example, wherein FIG. 22(a) isan LPP property diagram (graph) and FIG. 22(b) is an explanatory diagramfor illustrating conditions thereof;

FIGS. 23(a) through 23(c) illustrate a portion of an optical informationrecording medium of the conventional optical information recordingmedium, wherein FIG. 23(a) is a plan view of the recording medium, FIG.23(b) is a cross-sectional view taken along line 1 and FIG. 23(c) is across-sectional view taken along line 2;

FIGS. 24(a) and 24(b) show explanatory diagrams for illustratingprinciples of reproducing a phase pit in a related-art recording medium,wherein FIG. 24(a) is a plan view of the phase pit and FIG. 24(b) is awaveform diagram of the push-pull signal;

FIGS. 25(a) and 25(b) show explanatory diagrams for illustratingprinciples of reproducing a phase pit accompanying tracking in arelated-art recording medium, wherein FIG. 25(a) is a plan view of thephase pit and FIG. 25(b) is a waveform diagram of the push-pull signal;and

FIGS. 26(a) and 26(b) show explanatory diagrams for illustrating arelated-art recording medium in which the phase pit cannot be reproducedreliably, wherein FIG. 26(a) is a plan view of the phase pit and FIG.26(b) is a waveform diagram of the push-pull signal.

DESCRIPTION OF PREFERRED EMBODIMENTS

In describing preferred embodiments illustrated in the drawings,specific terminology is employed for clarity. However, the disclosure ofthis patent specification is not intended to be limited to the specificterminology selected and it is to be understood that each specificelement includes all technical equivalents that operate in a similarmanner.

According to one exemplary embodiment, an optical information recordingmedium is provided in which a track for recording the information is agroove and pre-format information is formed thereat as a phase pit. Thephase pit is formed at the groove and its radial cross section isasymmetrical relative to the track center of the groove.

Consequently, in such structure, since the phase pits are formed at thegroove and the shape of those phase pits in radial section isasymmetrical relative to the groove track center, when tracking controlis carried out utilizing the push-pull method, the signals reproduced(read) from the groove and the phase pit can be distinguished from eachother so that the phase pit information can be read (reproduced).

The phase pit is formed at the groove, and even when two phase pits areradially adjacent at adjacent grooves, they do not cause significantmutual interference. The phase pits are in the groove area and even ifthey protrude somewhat in the radial direction from the groove area,they can still be read reliably because they do not extend into the areaof an adjacent groove.

Another embodiment relates to an optical information recording medium inwhich a track for recording the information is a groove and pre-formatinformation is formed thereat as phase pits. The track center of thegroove is the same as the center of the phase pit, the width of thegroove is the same as that of the phase pit, and the groove depth of thegroove is the same as that of the phase pit. The inclination angles ofthe sides of the phase pit in radial section are different from eachother.

Consequently, by causing the inclination angles of the sides of thephase pit in radial section to differ from each other and thereby makingasymmetric the shape of the groove cross sections relative to the trackcenter, the phase pit can be kept from extending into an adjacentgroove, and phase pits that are radially adjacent can still be read outreliably.

Another embodiment relates to an optical information recording medium inwhich a track for recording the information is a groove and pre-formatinformation is formed thereon as phase pits. The center of the phase pitis shifted radially from the track center of the groove, the width ofthe phase pit is less than that of the groove, and the inclinationangles of the sides of the phase pit in radial section are equal to eachother.

Consequently, by reducing the width of the phase pit relative to thewidth of the groove, shifting the center of the phase pit radially fromthe track center, and causing the shape of the phase pit to beasymmetric relative to the track center, the phase pit is prevented fromextending into the groove(s) of the track(s) adjacent thereto and can beread reliably even when radially adjacent to another phase pit.

Another embodiment relates to an optical information recording medium inwhich a track for recording the information is a groove and pre-formatinformation is formed thereon as phase pits. The center of the phase pitis shifted radially from the track center of the groove, the width ofthe phase pit is greater than that of the groove but the phase pit doesnot extend radially into an adjacent groove, the groove depth of thegroove is equal to that of the phase pit, and the inclination angles ofsides of the phase pit in radial section are different from each other.

Consequently, by causing the inclination angles of the sides of thephase pit in radial section to differ from each other, widening thegroove width of the phase pit but not so much as to make the phase pitextend into an adjacent groove, and making asymmetric the shape of thephase pit in radial section relative to the track center, the phase pitcan be read reliably even when radially adjacent to another phase pit.

Another embodiment relates to an optical information recording medium inwhich a track for recording the information is a groove and pre-formatinformation is formed thereon as phase pits. The center of the phase pitis shifted radially from the track center of the groove withoutextending the phase pit into an adjacent groove, the width of the grooveis equal to that of the phase pit, the groove depth of the groove isalso equal to that of the phase pit, and the inclination angles of thesides of the phase pit in radial section are different from each other.

Consequently, by causing the inclination angles of the sides of thephase pit in radial section to differ from each other, shifting thephase pit radially without extending it into an adjacent groove, andmaking asymmetrical the shape of the phase pit in radial sectionrelative to the track center, the phase pit can be read reliably.

Another embodiment relates to an optical information recording medium inwhich a track for recording the information is a groove and pre-formatinformation is formed thereon as phase pits. The center of the phase pitis shifted radially from the track center, the width of the phase pit isgreater than that of the groove without allowing the phase pit to extendinto an adjacent groove, the depth of the groove is equal to that of thephase pit, and the inclination angles of the sides of the phase pit inradial section are equal to each other.

Consequently, by widening the phase pit without allowing it to extendinto an adjacent groove, and making asymmetric the shape of the phasepit radial section relative to the track center, the phase pit can beread reliably even when radially adjacent to another phase pit.

Another embodiment relates to an optical information recording medium inwhich a track for recording the information is a groove and pre-formatinformation is formed thereon as phase pits. The center of the phase pitis shifted radially from the track center of the groove withoutextending the phase pit into an adjacent groove, the width of the grooveis equal to that of the phase pit, and the depth of the groove is alsoequal to that of the phase pit, and the inclination angles of the sidesof the phase pit in radial section are equal to each other.

Consequently, by shifting the phase pit radially without extending itinto an adjacent groove, and making asymmetric the shape of the phasepit in radial section relative to the track center, the phase pit can beread reliably even when radially adjacent to another phase pit.

Another embodiment relates to a method of exposing a master formanufacturing the optical information recording medium as defined in thesecond embodiment and comprising the steps of: using two exposing lightbeams, namely, a groove exposing light beam centered at the center of atrack and a phase pit exposing light beam centered at a positionradially spaced from the center of the track; exposing a master by useof the groove exposing light beam when forming a groove; andsimultaneously exposing the master by use of the groove exposing lightbeam having a lower light intensity than when exposing a groove and thephase pit exposing light beam having another light intensity lower stillthan that of the groove exposing light beam, when exposing the phasepit.

Because the master can be exposed for forming the groove and the phasepit by controlling the distance between the two exposing light beam andthe light intensities of the exposing light beams, the phase pit can beformed reliably and precisely.

Another embodiment relates to a method of exposing a master formanufacturing the optical information recording medium as defined in thethird embodiment and comprising the steps of: using two exposing lightbeams having equal light intensities and spaced from each otherradially; arranging the two exposing light beams radially symmetricallyabout the center of a track and simultaneously exposing the master tothe two beams when exposing the groove; and shifting only one of theexposing light beams radially to reduce the spacing between the twobeams and simultaneously exposing the master for exposing the phase pit.

Because the distance between the two beams and the light intensities ofthe exposing light beams can be controlled, the phase pits can be formedreliably and precisely.

Another embodiment relates to a method of exposing a master formanufacturing the optical information recording medium as defined in thethird embodiment, comprising the steps of: centering an exposing lightbeam at the center of a track and exposing the master to form a groove;and shifting the exposing light beam radially from the center of thetrack and exposing the master with lower light intensity to form thephase pit.

Because of the control over the radial shifting of the exposing lightbeam and the light intensity of the exposing light beam, the phase pitcan be formed reliably and precisely.

Another embodiment relates to a method of exposing a master formanufacturing the optical information recording medium as defined in thefourth embodiment and comprising the steps of: using two exposing lightbeams, a groove exposing light beam centered at the center of track anda phase pit exposing light beam centered at a position radially shiftedfrom the center of the track; exposing a master by use of the grooveexposing light beam to form a groove; and simultaneously exposing themaster by use of the groove exposing light beam having a lower lightintensity and the phase pit exposing light beam having a lower stilllight intensity to form a phase pit.

Because of the control over the distance between the two exposing lightbeams and the light intensities of the exposing light beams, the phasepit can be formed reliably and precisely.

Another embodiment relates to a method of exposing a master formanufacturing the optical information recording medium as defined in thefifth embodiment and comprising the steps of: using two exposing lightbeams, a groove exposing light beam centered at the center of track anda phase pit exposing light beam at a position shifted radially from thecenter of the track; exposing a master by use of the groove exposinglight beam when forming a groove; and shifting radially the grooveexposing light beam and lowering its light intensity and using ittogether with the phase pit exposing light beam to expose the master forforming a phase pit.

Because of the control over the distance between the two exposing lightbeams and the light intensities of the exposing light beams, the phasepit can be formed reliably and precisely.

Another embodiment relates to a method of exposing a master formanufacturing the optical information recording medium as defined in thesixth embodiment and comprising the steps of: using an exposing lightbeam at the center of a track and exposing the master therewith forforming a groove; and shifting radially the exposing light beam exposingthe master at a higher light intensity for forming the phase pits.

Because of the control over the shifting and the light intensity of theexposing light beams, the phase pit can be formed well.

Another embodiment relates to a method of exposing a master formanufacturing the optical information recording medium as defined in thesixth embodiment and comprising the steps of: using two exposing lightbeams having equal light intensity and spaced from each other radially;arranging the two exposing light beams symmetrically radially relativeto the center of track and simultaneously exposing by use of the twoexposing light beams when forming a groove; and shifting only one of theexposing light beams to increase its distance from the other beam andsimultaneously exposing the original board to form the phase pitreliably.

Another embodiment relates to a method of exposing a master formanufacturing the optical information recording medium as defined in theseventh embodiment and comprising the steps of: using an exposing lightbeam of constant light intensity; disposing the exposing light beam atthe center of the track and exposing the original board to form agroove; and shifting the exposing light beam in the radius directionfrom the center of the track and exposing the master to form a phase pitreliably.

A first embodiment is described hereinafter referring to FIGS. 1(a)through 4(c). In the first as well as in the other embodiments, thegroove employed as the information recording track is labeled G, theland between adjacent grooves G is L, the phase pit signifyingpre-format information is P, the groove width of the groove G is Wg, andthe width of the phase pit P is Wp.

In the optical information recording medium of the first embodiment, thephase pit P is formed on the groove G. The inclination angles on therespective right and left sides of the phase pit P in the radiusdirection (perpendicular to the length of the track Tr) are madedifferent from each other. Namely, assuming that the respectiveinclination angles of the sides of the phase pit P are θ1 and θ2, thoseangles are not equal (θ1≠θ2, here θ1<θ2).

The inclination angles of the sides of the groove G are set to θ2. Inother respects, the phase pit P and the groove G are the same. Namely,the groove width Wg at the top of the groove G and the width Wp at thetop of the phase pit P are the same (Wg=Wp), although this does notalways need to be the case. The groove G and the phase pit P are equallydeep. Furthermore, the center of the width Wp of the phase pit Pcoincides with the track center of the groove G.

As compared with a conventional optical information recording medium asshown in FIGS. 23(a) through 23(c), the phase pit P of the firstembodiment is directly formed on the groove G instead of forming it onthe land L, and the inclination angles θ1 and θ2 of the sides of thephase pit P are made different from each other. Thereby, the crosssection of the phase pit P is made asymmetrical relative to the centerof track G. Consequently, for instance as shown at tracks Tr3 and Tr4,even though there are two phase pits P next to each other in the radialdirection at two adjacent tracks G, it is possible to arrange thosephase pits P, with their asymmetrical shape, next to each other in theradial direction. Therefore, those phase pits P can be stably reproducedand detected from the push-pull signal without being affected by theinterference between them.

Therefore, a large number of such optical information recording discscan be replicated utilizing an injection molding method using a metal“stamper”. Such a stamper can be made in accordance with the stampermanufacturing process as illustrated in FIG. 2. In this process, aphotoresist film 2 is applied and cured on a glass master substrate 1 tostart forming a glass master 3. Refer to FIG. 2(a). Next, the master 3is exposed to a focused laser beam, e.g., an Ar laser 4 in thisembodiment, to form a latent image therein corresponding to the locationof grooves G. Refer to FIG. 2(b). The exposed resist-covered master 3 isdeveloped to thereby form a groove pattern 5 in the photoresist film 2.Refer to FIG. 2(c). An Ni film is formed thereon, e.g., by sputtering,to thereby form an electrically conductive film 6 on the surface of themaster 3 having the groove pattern 5 formed on the photoresist film 2thereof. Refer to FIG. 2(d). A thicker Ni layer is formed (for example,by electrolytic deposition) on the conductive film 6 to thereby form aNi plate 7 thereon. Refer to FIG. 2(e). The Ni plate 7 is peeled offform the glass base plate 1. The plate 7 thus peeled off is completed asa stamper 8 by cleaning, rear surface polishing, inner diameter surfacetreatment, and outer diameter surface treatment. Refer to FIG. 2(f).

The process of exposing the photoresist layer on master 3, illustratedin FIG. 2(b), is further illustrated in FIG. 3. The master 3 is rotatedby a turn table 9 while being conveyed laterally, and the laser beam ofan Ar laser 4 is focused onto the resist layer on master 3. In this way,a groove pattern 5 matching the position of the grooves G is formed,e.g., as a spiral. The reference numeral 10 identifies an object lens.

The exposure of the resist layer on the master 3 to form a latent imageof recording track grooves G and phase pits P is further illustrated inFIGS. 4(a) through 4(c). In the present embodiment, two beams ofexposing light are employed for exposing the groove G and the phase pitP. One of them is a groove exposing light beam PWg aligned with thetrack center of the groove G, and the other is a phase pit exposinglight beam PWp spaced or shifted from beam PWg by a distance BD in theradius direction from the center of the track.

When only a groove G is being exposed, the resist on master 3 is exposedby use of only the groove exposing light beam PWg centered on the trackcenter, as shown by dot-and-dash line in FIG. 4(a). When the lightintensity of the groove exposing light beam PWg is decreased, the sidesof the groove G have smaller inclination angles, as illustrated in FIG.4(b). This illustrates the principle of controlling the inclinationangles of the groove sides by controlling the light intensity of theexposing light beam. When a phase pit is exposed, the light intensity ofthe groove exposing light beam PWg is reduced as compared with exposinga groove G, as illustrated in FIG. 4(c), and the phase pit exposinglight beam PWp spaced in the radial direction by the distance BD fromthe center of the track is used concurrently increase the inclinationangle of one side [in FIG. 4(c), right side], so that the resist onmaster 3 is exposed at the same time with the two exposing light beamsPWg and PWp. As seen in FIG. 4(c), the light intensity of the phase pitexposing light beam TWp is set to a value smaller than the lightintensity of the groove exposing light beam PWg.

In this manner, it is possible to form a phase pit P such that, as seenin FIGS. 1(b) and 1(c), its sides are asymmetrical relative to the trackcenter of the groove G, the groove width Wp of the phase pit P issubstantially the same as the groove width Wg of the groove G, and therelationship between the inclination angles θ1 and θ2 at the right andleft sides of the phase pit P becomes:

-   -   θ1<θ2.

A second embodiment is described hereinafter referring to FIGS. 5 athrough 6(b).

In the optical information recording medium of the second embodiments,the phase pit P is formed on the groove G, and the center of the phasepit P (the center of the groove cross section in the radial direction)is shifted by the distance s in the radius direction from the trackcenter of the groove G. Furthermore, the groove width Wp of the phasepit P is set to a value smaller than that of the groove width Wg(Wg>Wp), and the groove depths of the phase pit P and the groove G areset to an equal value.

The inclination angles of the sides of the phase pit P in a radialsection perpendicular to the length of the track Tr, are also set to anequal value. (The inclination angles of the sides of the groove G in asimilar section are set to another equal value.) As compared with aconventional optical information recording medium as shown in FIG. 23,in this second embodiment the phase pit P is not formed on the land L,and instead the groove width Wp of the phase pit P is made somewhatsmaller than that (Wg) of the groove G and the center of the phase pit Pis shifted by the distance s from the track center, and thereby thecross section of the phase pit P can be made offset from the trackcenter of the groove G. Consequently, for instance as shown in thetracks Tr3 and Tr4, two phase pits P exist side-by-side radially atadjacent tracks. Those phase pits P can be stably reproduced anddetected from the push-pull signal without interfering with each other.

A method of exposing the resist on master 3 for forming the groove Gincluding the phase pit P of this second embodiment status, illustratedin FIGS. 5(a)-5(c), is described hereinafter referring to FIGS. 6(a) and6(b). Two exposing light beams PW1 and PW2 are employed for exposing thegroove G and the phase pit P. The light intensities of those exposinglight beams PW1 and PW2 are set to a same value but the two beams areoffset from each other by the distance BD in the radius direction.

When exposing a groove G, the exposing light beams PW1 and PW2 are atposition flanking the track center of the groove G symmetrically in theradius direction (the track center is shown by the dot-and-dash line),and the resist on master 3 is exposed at the same time by the twoexposing light beams PW1 and PW2, as illustrated in FIG. 6(a).

When exposing a phase pit, one of the exposing light beams PW1 isshifted radially to reduce the distance BD between the two beams, asillustrated in FIG. 6(b), and the resist original board 3 is exposed atthe same time by those exposing light beams PW1 and PW2.

In this manner, it is possible to form the phase pit P such that thecenter of the phase pit P is shifted radially by a distance s from thetrack center of the groove G, the groove width of the phase pit P issmaller than that of the groove G, and the phase pit is asymmetricalrelative to the track center.

Namely, by controlling the beam distance and the light intensity of thetwo exposing light beam PW1 and PW2, the resist on maser 3 to expose thelocation for a groove G or a phase pit P as needed and, therefore, astable phase pit P can be formed and read.

A third embodiment is described hereinafter, referring to FIG. 7.

The third embodiment relates to a method of exposing the resist on themaster 3 for forming grooves G and phase pits P in the configurationsillustrated in FIGS. 5(a) through 5(c). In this third embodiment, onlyone exposing light beam (here, the groove exposing light beam PWg) isemployed.

When exposing for the groove G, the groove exposing light beam PWg iscentered on the center of the track. This beam is shown by the solidline in FIG. 7. That is the same as in the case of FIG. 4(a).

When exposing for the phase pit P, the groove exposing light beam PWg isshifted by the distance s in the radius direction from the center of thetrack and the light intensity for exposing the phase pit is made lowerthan that for exposing the groove. This light beam is shown by thedotted line in FIG. 7.

In this manner, it is possible to form the phase pit P such that, asseen in FIGS. 5(b) and 5(c), the center of the phase pit P is shiftedradially by the distance s from the track center of the groove G, thegroove width of the phase pit P is smaller than that of the groove G,and the phase pit cross section is offset from and asymmetrical relativeto the track center.

Namely, by controlling the amount by which the exposing light bean isshifted radially and by controlling the light intensity of the lightbeam PWg, the resist on the master 3 can be exposed for forming thegroove G and the phase pit P, and a stable phase pit P can be formed. Afourth embodiment is described hereinafter, referring to FIGS. 8(a)through 9(b).

In the fourth embodiment, the phase pit P is formed on the groove G, andthe inclination angles of the sides of the phase pit P (right and left)differ in a section in the radius direction perpendicular to the trackTr. Namely, assuming that the inclination angles are θ1 and θ2,respectively, the relationship of θ1 and θ2 is: θ1≠θ2. (Here, therelationship thereof is θ1<θ2.)

The inclination angles of both sides of the groove G equal θ2, and thecenter of the phase pit P (the center of the radial cross section, atthe level of Wp) is shifted by the distance s in the radius directionfrom the track center of the groove G. The groove width Wp of the phasepit P is set to a value larger than that (Wg) of the groove G (Wg<Wp).The groove depths of both G and P are set to an equal value. Althoughthe groove width Wp of the phase pit P is larger than that (Wg) of thegroove G, the groove width Wp is set to the value within a range suchthat the phase pit P is not connected to the groove G of the adjacenttracks in the radial direction.

As compared with a conventional optical information recording medium asillustrated in FIG. 23, in this fourth embodiment a part of a phase pitP on a groove G and in part is on a land L adjoining that groove G, butthe position of the phase pit P and its width Wp are controlled suchthat the phase pit P does not extend radially to another land L oranother groove G. Thereby, the center of the phase pit P can be offsetfrom the center of the groove G, and the phase pit P can be madeasymmetrical in the radial direction relative to the center of thegroove G.

Therefore, for instance as shown at tracks Tr3 and Tr4 in FIGS. 8(a)through 8(c), even though two phase pits P exist at adjacent tracksradially next to each other, they are still spaced from each otherradially. Consequently, those phase pits P can be stably reproduced anddetected form the push-pull signal without causing mutual interference.

A method of exposing the resist on a master 3 for forming the grooves Gand the phase pits P of this fourth embodiment illustrated in FIGS. 8(a)through 8(c) is described hereinafter, referring to FIG. 9. Two exposinglight beams are employed in order to expose the groove G and the phasepit P. One of the beams is the groove exposing light beam PWg centeredat the track center of the groove G, and the other is the phase pitexposing light beam PWp shifted by the distance BD in the radiusdirection from the track center.

When exposing for the groove, the resist on master 3 is exposed by useof only the groove exposing light beam PWg centered at the track center(shown by the dot-and-dash line) as seen in FIG. 9(a). That is the sameas in FIG. 4(a).

When exposing for the phase pit, utilizing the principle controlling theinclination angles of the sides of the phase pit P by controlling thelight intensity of the exposing light beam as earlier discussed, thelight intensity of the groove exposing light beam PWg is made decreasedas compared with using it for exposing for the groove G as seen in FIG.9(b), and the exposing light beam PWp for the phase pit, centered at apoint shifted radially by the distance BD from the track center, is usedat the same time used in order to increase the inclination angle at oneside of the phase pit P [in FIG. 9(b), right side]. Thus, the resist onmaster 3 is exposed at the same time with the two exposing light beamsPWg and PWp.

As seen in FIG. 9(b), the light intensity of the phase pit exposinglight beam PWp is set to the value lower than that of the grooveexposing light beam PWg. Here, in comparison with the method of exposingthe original board for forming the phase pit P of the type seen in FIG.1, the distance BD between the exposing light beams PWg and PWp isgreater than that shown in FIG. 4(c), and the light intensity of thephase pit exposing light beam PWp is set to a somewhat higher value asshown by the dotted line in FIG. 9(b). Namely, in order to widen thegroove width Wp of the phase pit P radially, the distance between theexposing light beam PWg and PWp is made greater than that in the methodillustrated in FIG. 4, and the light intensity of the phase pit exposinglight beam is set to the value a somewhat greater than that of the phasepit exposing beam PWp of FIG. 4.

Though this process, it is possible to form the configurationillustrated in FIGS. 8(a) through 8(c), where the center of the phasepit P (at the level of width Wp) is shifted by the distance s from thetrack center of the groove G, the relationship between the inclinationangles θ1 and θ2 of the left and right sides of phase pit P is θ1<θ2,the groove width Wp of the phase pit P is greater than the width (Wg)the groove G, and the phase pit P's radial section is asymmetricalrelative to the track center.

Namely, since the resist on the master 3 for the groove G and that forthe phase pit P can be exposed by controlling the position and spacingand the light intensity of the he exposing light beams PWg and PWp, thephase pit P can be formed stably and precisely.

A fifth embodiment is described hereinafter, referring to FIGS. 10(a)through 11(b).

In the optical information recording medium of the fifth embodiment, thephase pit P is formed on the groove G and the inclination angles of thesides of the phase pit P (right and left) in the radius directionperpendicular to the track Tr, are made different from each other.Namely, assuming that the inclination angles at the edge portions arerespectively θ1 and θ2, the relationship between the angles is θ1≠θ2(here, θ1<θ2).

The inclination angles of the sides of the groove G are both equal toθ2. The center of the width Wp of the phase pit P is shifted by thedistance s in the radius direction from the track center of the grooveG. The widths Wg of the groove G and Wp of the phase pit P are the same(Wg=Wp), and the depths of both also are the same. The shift amount sfrom the track center of the phase pit P is set such that a phase pit Premains spaced from an adjacent groove G in the radial direction.

As compared with a conventional optical information recording medium ofthe type illustrated in FIG. 23, although in this fifth embodiment apart of the phase pit P extends radially to the land L, the shift amounts is controlled such that the phase pit P does not connect to the grooveG of the adjacent tracks, and the width Wp of the phase pit P can bemade asymmetrical relative to the track center of the groove G.Consequently, for instance, as seen at tracks Tr3 and Tr4, even thoughtwo phase pits P are next to each other in the radial direction on twoadjacent tracks, it is possible to arrange the phase pits P such thatthey remain radially spaced from each other and can be stably reproducedand detected from the push-pull signal without mutual interference.

The method of exposing the original board for forming the groove Gincluding the phase pit P of the present embodiment status as shown inFIG. 10 is described hereinafter, referring to FIG. 11. The presentembodiment status also uses the two lines of the exposing light beam forexposing the groove G and the phase pit P. One of those beams is thegroove exposing light beam PWg disposed on the track center of thegroove G, and another one of those beams is the phase pit exposing lightbeam PWp shifted by the distance BD in the radius direction from thetrack center.

When exposing the resist on the master 3 for forming the groove, onlyone groove exposing light beam PWg is used, centered at the track centeras shown by dot-and-dash line in FIG. 11(a). The method is same as thatof FIG. 4(a).

When exposing for forming the phase pit, utilizing the principle ofcontrolling the inclination angle of the sides of the phase pit bycontrolling the light intensity of the exposing light beam as mentionedbefore, as seen in FIG. 11(b), the light intensity of the grooveexposing light beam PWg is made smaller than that at the time ofexposing for forming the groove G, and the resist on master 3 is exposedat the same time with the two exposing light beams PWg and PWp, with thephase pit exposing light beam PWp spaced radially from the track center)by the spacing BD in order to increase the inclination angle of one sideof the phase pit P [in FIG. 11(b), right side].

As seen in FIG. 11(b), the light intensity of the phase pit exposinglight beam PWp is set to a lower value than that of the groove exposinglight beam PWg. In order to shift the center of the phase pit P in theradius direction from the track center, the two exposing light beam PWgand PWp are shifted at the same time by the distance s in the radiusdirection from the track center as shown by the dotted line in FIG.11(b).

By exposing the resist on the master 3 in this manner, it is possible toform the structure illustrated in FIGS. 10(a) through 10(c), where thecenter of the width Wp of the phase pit P is shifted radially by thedistance s from the track center of the groove G, the relationshipbetween the inclination angles θ1 and θ2 of sides of the phase pit P isθ1<θ2, and the phase pit P is asymmetrical relative to the track center.

Namely, since the resist on the master 3 can be exposed for forming thegroove G and the phase pit P by controlling the beam positions andspacing and the light intensity of the two exposing light beams PWg andPWp, the phase pit P can be stably and precisely formed.

A sixth embodiment is described hereinafter, referring to FIGS. 12 and13.

In the optical information recording medium of the sixth embodiment, thephase pit P is formed on the groove G and the center of the radial crosssection of the phase pit P is shifted by the distance s in the radiusdirection from the track center of the groove G. The groove width Wp ofthe phase pit P is greater than the groove width Wg of the groove G(Wg<Wp), and the depths of both are equal.

Although the width Wp of the phase pit P is more than the groove widthWg of the groove G, the width Wp is set such that the phase pit P doesnot connect to the groove G of the adjacent tracks. The inclinationangles of the sides of the phase pit P (right and left) in the radiusdirection perpendicular to the track Tr are set to an equal value. (Theinclination angles of the sides of the groove G also are equal.) Ascompared with a conventional optical information recording medium of thetype illustrated in FIG. 23, although the phase pit P of this sixthembodiment extends into a part of the land L, the width of the phase pitP in controlled such that the phase pit P does not connect to the grooveG of the adjacent tracks, and in radial cross section the phase pit P isasymmetrical relative to the track center of the groove G. Consequently,for instance, as shown by the tracks Tr3 and Tr4, even if two phase pitsP exist side-by-side in the radial direction at the adjacent tracks,those phase pits P can be stably reproduced and detected from thepush-pull signal without mutual interference.

A method of exposing the resist on the master 3 in order to form agroove G and a phase pit P according to this sixth embodiment, asillustrate in FIGS. 12(a) through 12(c) is described hereinafter,referring to FIGS. 13(a) and 13(b). Two exposing light beams PW1 and PW2are used for exposing the groove G and the phase pit P. The lightintensities of those exposing light beams PW1 and PW2 are set to anequal value, and the two beams are separated by the distance BD in theradius direction.

When the resist on the master 3 is being exposed for forming the groove,both of the exposing light beams PW1 and PW2 symmetrically flank thetrack center (shown by dot-and-dash line) in the radial direction, asseen in FIG. 13(a). The resist on the master 3 is exposed at the sametime with those exposing light beams PW1 and PW2. The method is same asthat of FIG. 6(a).

In order to expose the resist on the master 3 for forming the phase pitP, as shown by the dotted line in FIG. 13(b), the exposing light beamPW2 is shifted in a radial direction to increase the distance BD betweenthe two beams. The resist on the master 3 is exposed at the same timewith both exposing light beams PW1 and PW2.

By carrying out such exposure of the master 3 in order to form groovesand phase pits of the type illustrated in FIGS. 12(a) through 12(c), itis possible to form the phase pit P such that the center of the phasepit P is shifted radially by the distance s from the track center of thegroove G, the groove width Wp of the phase pit P is made greater thanthat (Wg) of the groove G, and the phase pit P has a radial crosssection that is asymmetrical relative to the track center. The resist onthe master 3 can be exposed for forming the groove G and the phase pit Pby controlling the distance between, and the light intensity of, the twoexposing light beam PW1 and PW2 so as to form the phase pit P stably andprecisely.

A seventh embodiment is described hereinafter, referring to FIG. 14. Theseventh embodiment relates to a method of exposing the resist on themaster 3 for forming a groove G and a phase pit P of the typeillustrated in FIGS. 12(a) through 12(c).

In the seventh embodiment, only one exposing light beam (here, thegroove exposing light beam PWg) is employed.

At the time of exposure for forming the groove, the groove exposinglight beam PWg is centered at the track center and the resist on themaster 3 is exposed as shown by the solid line in FIG. 14. The method issame as that of FIG. 4(a).

At the time or exposing the resist on the master 3 for forming the phasepit, the groove exposing beam PWg is shifted by the distance s in theradius direction from the track center and its light intensity isincreased as compared with the case of exposing the groove, as shown bythe dotted line in FIG. 14. The resist is exposed in this shiftedposition and at this increased intensity of the beam PWg in order toform the phase pit.

Though practicing this method of exposing the resist on the master 3, itis possible to achieve the configuration illustrated in FIGS. 12(a)through 12(c), where the center of the phase pit P is shifted by thedistance s from the track center, the phase pit groove width Wp of thephase pit P is greater than that (Wg) of the groove G, and the phase pitP has a radial cross sections that is asymmetrical relative to the trackcenter.

Namely, by controlling the degree of shifting and the light intensity ofthe groove exposing light beam PWg, the resist on the master 3 can beexposed appropriately for forming the groove G and the phase pit P, andthe phase pit P can be formed stably and precisely.

An eighth embodiment is described hereinafter, referring to FIGS. 5, 15and 16.

In an optical information recording medium according to the eighthembodiment, the phase pit P is formed at the groove G, and the center ofthe phase pit P (the center of the phase pit in a radial cross section)is shifted by the distance s in the radius direction from the trackcenter of the groove G. The shifting amount s of the phase pit P fromthe track center is selected such that the phase pit P is not connectedto the groove G of either adjacent track. The groove width Wg of thegroove G and that Wp of the phase pit P are set to an equal value(Wg=Wp). The groove depths of the groove G and the phase pit P are alsoset to another equal value. The inclination angles of the sides of thephase pit P (in a radial section perpendicular to the track Tr) are alsoset to an equal value.

As compared with a conventional optical information recording medium ofthe type illustrated in FIG. 23, in the 8th embodiment a part of thephase pit P is at a groove and a part is at a land but, cy controllingthe amount of offset or shifting, the phase pit is prevented fromconnecting to a groove G of an adjacent tracks. In radial section, thephase pit P is asymmetrical relative to the track center. Therefore, forinstance as shown at tracks Tr3 and Tr4, even if two phase pits P existside-by-side in the radial direction at two adjacent tracks, those phasepits P can be stably reproduced and detected from the push-pull signal,without mutual interference.

A method of exposing the resist on the master 3 for forming the groove Gand the phase pit P of the 8th embodiment, in the configurationillustrated in FIGS. 15(a) through 15(c), is described hereinafterreferring to FIG. 16. Only one exposing light beam (here, the grooveexposing light beam PWg) is employed.

At the time of exposing the resist on the master 3 for forming thegroove, the exposing light beam PWg is centered at the track center, asshown by the solid line in FIG. 16. The method is same as that of FIG.4(a).

For exposing the resist on the master 3 for forming the phase pit, thegroove exposing light beam PWg is shifted by the distance s from thetrack center, as shown by the dotted line in FIG. 16. The exposure forthe phase pit takes place with the beam so shifted.

Through this method of exposing the resist on the master 3 to achieve astructure of the type illustrated in FIGS. 12(a) through 12(c), it ispossible to form the phase pit P such that in radial section its centeris spaced radially by the distance s from the track center, and thephase pit P in radial section is asymmetrical relative to the trackcenter. Namely, by controlling the amount of offset or shift and thelight intensity of the groove exposing light beam, the phase pit P canbe formed stably and precisely.

Results

As earlier discussed in connection with FIGS. 25(a) and 25(b), there isa relationship between the shape and position of the phase pit Prelative to the groove G and the difference value A of the push-pullsignal at the phase pit. In the discussion below, a numerical value LPPis used for convenience, obtained by dividing the value A of thepush-pull signal by the sum signal (level) at the time of reading thegroove G (and the phase pits thereat). For reading, a reproducing beam Bis used comprising a laser beam having a wavelength of 635 nm and a beamdiameter of approximately 0.9 μm. The track pitch TP is approximately0.8 μm. Phase change recording material is used as the recording mediumalong the tracks, formed as a recording film on a substrate that carriesother layers as well, including a protective layer.

FIRST EXAMPLE

Results regarding the first embodiment, illustrated in FIGS. 1(a)through 1(c), are described hereinafter, referring to FIGS. 17(a) and17(b) illustrating the effect on LPP of varying the inclination angle θ1of one side (in radial section) of the phase pit P. In this example, theangle θ2 of the other side, e.g., the right-hand side in FIG. 17(b), isfixed at θ2=45°. The width Wp of the phase pit P is set to 0.4 μm andthe groove depth thereof is set to 600 A.

In FIG. 17(a), the mark “∘” represents the numerical value of LPP whenreading a phase pit when no other phase pit is radially adjacent theretoat an adjacent track, while the mark “·” represents the numerical valueof LPP when reading a phase pit that has another phase pit radiallyadjacent thereto at an adjacent track (so that the two phase pits thatare radially side-by-side can potentially interfere with each other).

In order to produce the appropriate configuration of grooves and phasepits through exposure of the resist on the master 3 for this example,two exposing light beams are used, as discussed in connection with FIGS.4(a) through 4(c), and samples that differ from each other in variousparameters can be made by suitably controlling the distance between theexposing light beams and the light intensities thereof.

According to the illustration of FIG. 17(a), when there is no radiallyadjacent phase pit to the one being read, in general the smaller theinclination angle θ1 at one side of the phase pit (in radial section),the greater the value of LPP, and the inclination angle of θ1≈10° yieldsa maximum value of LPP (LPP≈0.20).

As illustrated in FIG. 17(a), even when there is a radially adjacentphase pit at the next track, as shown by the mark “·”, the value of LPPdecreases by only up to approximately 0.05, in comparison with the caseshown by the mark “∘”. It can be appreciated that an inclination angleof θ1≈10° enhances the stability of the LLP signal and the stabledetection of the phase pits even when two phase pits are radiallyside-by-side at adjacent tracks.

SECOND EXAMPLE

Results regarding the second embodiment, illustrated in FIGS. 5(a)through 5(c), are described hereinafter, referring to FIGS. 18(a) and18(b) illustrating the effect on LPP of radially shifting only one side(in radial section) of the phase pit P to thereby reduce the width Wp ofthe phase pit P.

As illustrated in FIG. 18(b), both of the inclination angles θ1 and θ2at the sides (in radial section) of the phase pit are 45°. The width Wpand depth Dp of the phase pit P are respectively 0.4 μm and 600 A. InFIG. 18(a), the mark “∘” represents the numerical value of LPP fromreading a phase pit when no other phase pit is radially adjacent theretoat an adjacent track, while the mark “·” represents the numerical valueof LPP from reading a phase pit when another phase pit is radiallyadjacent thereto at an adjacent track (so that the two phase pits thatare radially side-by-side can potentially interfere with each other).Two exposing beams were used, as discussed in connection with FIGS. 6(a)and 6(b) to produce samples having different parameters by controllingthe distance between the exposing light beams and the light intensitiesthereof.

As illustrated in FIG. 18(a), even when there is a radially adjacentphase pit at the next track, as shown by the mark “·”, the value of LPPdecreases by only up to approximately 0.05, in comparison with the caseas shown by the mark “∘”. It can be appreciated that the presence of tworadially adjacent phase pits does not cause significant interference.

In the case of the second embodiment, it is preferable that the width Wpof the phase pit P be approximately 0.2 μm and the center (in radialsection) of the phase pit be shifted radially from the track center byapproximately 0.06 μm.

THIRD EXAMPLE

Results related to the fourth embodiment, illustrated in FIGS. 8(a)through 8(c), are described hereinafter, referring to FIGS. 19(a) and19(b). In that fourth embodiment, the inclination angles θ1 and θ2 at ofthe sides (in radial section) of the phase pit are different from eachother. FIGS. 19(a) and 19(b) illustrate the effect on LPP of shiftingonly ones side of the phase pit P to thereby increase the width Wp(while maintaining the two different inclination angles).

As illustrated in FIG. 19(b), the inclination angles are:

-   -   θ1=10°, and θ2=45°.

The depth Dp of the phase pit P is 600 A. In FIG. 19(a), the mark “∘”represents the numerical value of LPP from reading a phase pit when noother phase pit is radially adjacent thereto at an adjacent track, whilethe mark “·” represents the numerical value of LPP from reading a phasepit when another phase pit is radially adjacent thereto at an adjacenttrack (so that the two phase pits that are radially side-by-side canpotentially interfere with each other). Two exposing beams were used, asdiscussed in connection with FIGS. 9(a) and 9(b) to produce sampleshaving different parameters by controlling the distance between theexposing light beams and the light intensities thereof.

As illustrated in FIG. 19(a), even when there is a radially adjacentphase pit at the next track, as shown by the mark “·”, the value of LPPdecreases by only up to approximately 0.05, in comparison with the caseas shown by the mark “∘”. It can be appreciated that the presence of tworadially adjacent phase pits does not cause significant interference.

As seen in FIG. 19(a), in the case of the fourth embodiment (FIGS.8(a)-8(c)) it is preferable that the width Wp of the phase pit P begreater than in the case of the first embodiment (FIGS. 1(a) through1(c)) and that the center of the phase pit (in radial section) beshifted in the arrow direction, so as to increase the value of LLP. Asuitable width Wp is approximately 0.65 μm.

In order to ensure reliably that no phase pit P extends into a groove Gof an adjacent tracks, it is preferable to keep the width Wp of thephase pit P in the range of 0.5 through 0.7 μ?m when a track pitch PT ofapproximately 0.8 μm is used, taking into account probabilities inherentin manufacturing such as those involving variations in the track pitchTP and light intensity variation of the respective beams.

FOURTH EXAMPLE

Results related to the fifth embodiment, illustrated in FIGS. 10(a)through 10(c)), are described hereinafter referring to FIGS. 20(a) and20(b). In the fifth embodiment, the inclination angles θ1 and θ2 at thesides (right and left) in a radial section through the phase pit aredifferent from each other, where

-   -   θ1=10°, and θ2=45°

The width Wp of the phase pit P is 0.4 μm, as is the groove G, and thedepth Dp of the phase pit is 600 A. In FIG. 20(a), the mark “∘”represents the numerical value of LPP from reading a phase pit when noother phase pit is radially adjacent thereto at an adjacent track, whilethe mark “·” represents the numerical value of LPP from reading a phasepit when another phase pit is radially adjacent thereto at an adjacenttrack (so that the two phase pits that are radially side-by-side canpotentially interfere with each other). Two exposing beams were used, asdiscussed in connection with FIGS. 11(a) and 11(b) to produce sampleshaving different parameters by controlling the distance between theexposing light beams and the light intensities thereof.

As illustrated in FIG. 20(a), as the phase pit P is shifted further fromthe track center in the radius direction, the value of LPP increasesuntil the shift reaches approximately 0.15 μm, and the value of LLP isoptimum at approximately that range.

FIFTH EXAMPLE

Results regarding the sixth embodiment, illustrated in FIGS. 12(a)through 12(c), are discussed below in connection with FIGS. 21(a) and21(b). In the sixth embodiment, the inclination angles θ1 and θ2 of thesides (right and left) of the phase pit in radial section are equal toeach other, e.g.

-   -   θ1=θ2=45°.    -   the depth Dp of the phase pit P is 600 A and the widths Wp and        Wg are the same. FIG. 21(a), illustrates the effect on the value        of LLP of shifting only the one side (in radial section) of the        phase pit P to thereby increase the width Wp of the phase pit P,        where the mark “∘” represents the numerical value of LPP from        reading a phase pit when no other phase pit is radially adjacent        thereto at an adjacent track, while the mark “·” represents the        numerical value of LPP from reading a phase pit when another        phase pit is radially adjacent thereto at an adjacent track (so        that the two phase pits that are radially side-by-side can        potentially interfere with each other). Two exposing beams were        used, as discussed in connection with FIGS. 13(a) and 13(b) to        produce samples having different parameters by controlling the        distance between the exposing light beams and the light        intensities thereof. As illustrated in FIG. 20(a), as the phase        pit P is made wider and the center thereof (in radial section)        is shifter more from the track center, the value of LPP        increases until the value of LLP becomes optimal at        approximately 0.60 μm shift, where the value of LLP is        approximately 0.40 when two phase pits are side-by-side in the        radial direction at two adjacent tracks.

SIXTH EXAMPLE

Results regarding the eighth embodiment, illustrated in FIGS. 15(a)through 15(c), are discussed below in connection with FIGS. 22(a) and22(b). In the eighth embodiment, the inclination angles θ1 and θ2 of thesides (right and left) of the phase pit in radial section are equal toeach other, e.g.

-   -   θ1=θ2=45°.    -   the depth Dp of the phase pit P is 600 A and the widths Wp and        Wg are the same. FIG. 22(a), illustrates the effect on the value        of LLP of shifting the phase pit P in the radial direction        relative to the track, where the mark “∘” represents the        numerical value of LPP from reading a phase pit when no other        phase pit is radially adjacent thereto at an adjacent track,        while the mark “·” represents the numerical value of LPP from        reading a phase pit when another phase pit is radially adjacent        thereto at an adjacent track (so that the two phase pits that        are radially side-by-side can potentially interfere with each        other). One exposing beam was used, as discussed in connection        with FIG. 16 to produce samples having shift values.

As illustrated in FIG. 22(a), as the center (in radial section) of thephase pit P is shifted further in the radial direction from the trackcenter, the value of LPP increases until the value of LLP becomesoptimal at approximately 0.20 μm shift, where the value of LLP isapproximately 0.40 when two phase pits are side-by-side in the radialdirection at two adjacent tracks.

According to a first aspect of the disclosed optical informationrecording media, since the phase pit is formed at the groove and theshape of the phase pit in a radial section is made asymmetrical relativeto the track center of the groove, the phase pit can be reliablydistinguished from the rest of the groove when reproducing the signaland tracking the groove utilizing the push-pull method. Although thephase pit is formed at the groove, there is no significant mutualinterference between phase pits even when they are radially adjacent atadjacent tracks.

According to a second aspect of the disclosed optical informationrecording media, only by making different from each other theinclination angles of the phase pit sides (in radial section) andthereby making asymmetrical the shape of the groove in radial sectionrelative to the track center, the phase pit can be kept from encroachingon the grooves of adjacent tracks and thereby prevent significant mutualinterference between phase pits even when they are radially adjacent atadjacent tracks.

According to a third aspect of the disclosed optical informationrecording media, the center of the phase pit is shifted from the trackcenter of the groove in the radius direction perpendicular to the track,the width of the phase pit is smaller than that of the groove, thedepths of the phase pit and the groove are equal to each other, and theinclination angles of the sides of the phase pit in radial section areequal to each other.

Consequently, only by making the width of the phase pit smaller thanthat of the groove, shifting the center of the phase pit radially fromthe track center and thereby obtaining a phase pit which in radialsection is asymmetrical relative to the track center, the phase pit canbe kept from extending to the groove of an adjacent track, and therebythe phase pit can be read reliably, without significant interferenceeven when there are two radially adjacent phase pits at adjacent tracks.

According to a fourth aspect of the disclosed optical informationrecording media, the inclination angles of the sides of the phase pit inradial section are made different from each other, the width of thephase pit is increased but not so much such that the phase pit extendsto the groove of the adjacent track, and the shape of the radialsections thereof is made asymmetrical relative to the track center.Thus, the phase pit is kept from extending into the groove of anadjacent track, and the phase pit can be reliably read withoutsignificant interference even when two phase pits are radially adjacentat adjacent tracks.

According to a fifth aspect of the disclosed optical informationrecording media, the inclination angles of the sides of the phase pit inradial section are made different from each other, the phase pit isshifted in the radius direction but not so much such that it extendsinto the groove of an adjacent tracks, and the radial section thereof ismade asymmetrical relative to the track center. Thus, the phase pit iskept from extending into the groove of an adjacent tracks, and the phasepit can be reliably read without significant interference even when twophase pits are radially adjacent at adjacent tracks.

According to a sixth aspect of the disclosed optical informationrecording media, the width of the phase pit is increased but not so muchsuch that the phase pit extends into the groove of an adjacent tracks,and the radial section thereof is made asymmetrical relative to thetrack center. Thus, the phase pit is kept from extending into the grooveof an adjacent tracks, and the phase pit can be reliably read withoutsignificant interference even when two phase pits are radially adjacentat adjacent tracks.

According to a seventh aspect of the disclosed optical informationrecording media, the phase pit is shifted in the radius direction butnot so much such that it extends into the groove of an adjacent track,and the radial section thereof is made asymmetrical relative to thetrack center. Thus, the phase pit is kept from extending into the grooveof an adjacent track, and the phase pit can be reliably read withoutsignificant interference even when two phase pits radially adjacent attwo adjacent tracks.

According to an eighth aspect of the disclosed optical informationrecording media, since the master can be exposed for forming the grooveand the phase pit by controlling the distance between two exposing lightbeams and the light intensities thereof, the phase pit can be reliablyand precisely formed at the time of manufacturing an optical informationrecording medium according to the second aspect of the disclosed media.

According to a ninth aspect of the disclosed optical informationrecording media, since the master can be exposed for forming the grooveand the phase pit by controlling the distance between two exposing lightbeams and the light intensities thereof, the phase pit can be formedreliably and precisely at the time of manufacturing the opticalinformation recording medium according to the third aspect of thedisclosed media.

According to a tenth aspect of the disclosed optical informationrecording media, since the master can be exposed for forming the grooveand the phase pit by controlling the radial shifting of one exposinglight beam and the light intensity thereof, the phase pit can be formedreliably and precisely at the time of manufacturing an opticalinformation recording medium as defined in the third aspect of thedisclosed media.

According to an eleventh aspect of the disclosed optical informationrecording media, since the master can be exposed for forming the grooveand the phase pit by controlling the distance between two exposing lightbeams and the light intensities thereof, the phase pit can be formedreliably and precisely at the time of manufacturing the opticalinformation recording medium as defined in the fourth aspect of thedisclosed media.

According to a twelfth aspect of the disclosed optical informationrecording media, since the master can be exposed for forming the grooveand the phase pit by controlling the distance between two exposing lightbeams and the light intensities thereof, the phase pit can be formedreliably and precisely at the time of manufacturing the opticalinformation recording medium as defined in the fifth aspect of thedisclosed media.

According to a thirteenth aspect of the disclosed optical informationrecording media, since the master can be exposed for forming the grooveand the phase pit by controlling the degree of radially shifting oneexposing light beam and the light intensity thereof, the phase pit canbe formed reliably and precisely at the time of manufacturing theoptical information recording medium as defined in the sixth aspect ofthe disclosed media.

According to a fourteenth aspect of the disclosed optical informationrecording media, since the master can be exposed for forming the grooveand the phase pit by controlling the distance between two exposing lightbeams and the light intensities thereof, the phase pit can be formedreliably and precisely at the time of manufacturing the opticalinformation recording medium as defined in the sixth aspect of thedisclosed media.

According to a fifteenth aspect of the disclosed optical informationrecording media, since the master can be exposed for forming the grooveand the phase pit by controlling the degree of radially shifting oneexposing light beam and the light intensity thereof, the phase pit canbe formed reliably and precisely at the time of manufacturing theoptical information recording medium as defined in the seventh aspect ofthe disclosed media.

The above specific embodiments are illustrative, and many variations canbe introduced on these embodiments without departing from the spirit ofthe disclosure or from the scope of the appended claims. It is thereforeto be understood that within the scope of the appended claims, thedisclosed material may be practiced otherwise than as specificallydescribed herein. For example, elements and/or features of differentillustrative embodiments may be combined with each other and/orsubstituted for each other within the scope of this disclosure andappended claims.

This application is based on Japanese Patent Application No.JPAP-09-230696, filed on Aug. 27, 1997, the entire contents of which areincorporated by reference herein.

1. An optical information recording medium comprising: informationrecording tracks configured to serve as grooves; and phase pits formedon the tracks in a way such that radially opposite edge portions of thephase pits orthogonal to the tracks have tilt angles different from eachother, wherein preformatted information is recorded as said phase pits.2. An optical information recording medium comprising: groovesconfigured to serve as information recording tracks; and phase pitsformed on the tracks in a way such that radially opposite edge portionsof the phase pits orthogonal to the tracks have tilt angles differentfrom each other, wherein preformatted information is recorded as saidphase pits, and wherein a track center of the grooves and a center ofthe phase pits are substantially identical, gap widths of the groovesand the phase pits are substantially identical, and gap depths of thegrooves and the phase pits are substantially identical.
 3. An opticalinformation recording medium comprising: grooves configured to serve asinformation recording tracks; and phase pits formed on the tracks in away such that radially opposite edge portions of the phase pitsorthogonal to the tracks have tilt angles different from each other,wherein preformatted information is recorded as said phase pits, andwherein a center of the phase pits is radially displaced relative to atrack center of the grooves, a gap width of the phase pits is greaterthan a gap width of the grooves such that each of the phase pits leavesa radial clearance from an immediately adjacent one of the grooves, andgap depths of the grooves and the phase pits are substantiallyidentical.
 4. An optical information recording medium comprising:grooves configured to serve as information recording tracks; and phasepits formed on the tracks in a way such that radially opposite edgeportions of the phase pits orthogonal to the tracks have tilt anglesdifferent from each other, wherein preformatted information is recordedas said phase pits, and wherein a center of the phase pits is radiallydisplaced relative to a track center of the grooves such that each ofthe phase pits leaves a radial clearance from an immediately adjacentone of the grooves, gap widths of the grooves and the phase pits aresubstantially identical, and gap depths of the grooves and the phasepits are substantially identical.
 5. An original medium exposing methodfor producing the optical information recording medium of claim 2, saidmethod comprising the steps of: arranging a groove exposure beam at atrack-center oriented position; arranging a phase pit exposure beam at aplace radially displaced from a track center; conducting a grooveexposure with the groove exposure beam; and conducting a phase pitexposure substantially simultaneously with the groove exposure, whereinin a time of the phase pit exposure, a light amount of the grooveexposure beam is reduced, and a light amount of the phase pit exposurebeam is smaller than the reduced light amount of the groove exposurebeam.
 6. An original medium exposing method for producing an opticalinformation recording medium, said method comprising the steps ofconducting a groove exposure for exposing an original medium with anexposure beam by arranging the exposure beam at a track-center orientedposition; and conducting a phase pit exposure for exposing the originalmedium with the exposure beam slightly displaced in a radial directionfrom the track-center oriented position, wherein a light amount of thephase pit exposure is reduced from a light amount used in the grooveexposure, wherein, in the optical information recording medium, groovesserve as information recording tracks and phase pits are formed aspreformatted information on the tracks in a way such that radiallyopposite edge portions of the phase pits orthogonal to the tracks havetilt angles different from each other, and wherein a center of the phasepits is radially displaced relative to a track center of the grooves, agap width of the phase pits is smaller than a gap width of the grooves,and gap depths of the grooves and the phase pits are substantiallyidentical.
 7. An original medium exposing method for producing theoptical information recording medium of claim 3, said method comprisingthe steps of: arranging a groove exposure beam at a track-centeroriented position; arranging a phase pit exposure beam at a placeradially displaced from a track center; conducting a groove exposurewith the groove exposure beam; and conducting a phase pit exposuresubstantially simultaneously with the groove exposure, wherein in a timeof the phase pit exposure, a light amount of the groove exposure beam isreduced and a light amount of the phase pit exposure beam is smallerthan the reduced light amount of the groove exposure beam.
 8. Anoriginal medium exposing method for producing the optical informationrecording medium of claim 4, said method comprising the steps of:arranging a groove exposure beam at a track-center oriented position;arranging a phase pit exposure beam at a place radially displaced from atrack center; conducting a groove exposure with the groove exposurebeam; and conducting a phase pit exposure substantially simultaneouslywith the groove exposure, wherein in a time of the phase pit exposure, alight amount of the groove exposure beam is reduced and a light amountof the phase pit exposure beam is smaller than the reduced light amountof the groove exposure beam.
 9. An original medium exposing method forproducing an optical information recording medium, said methodcomprising the steps of: conducting a groove exposure for exposing anoriginal medium with an exposure beam by arranging the groove exposurebeam at a track-center oriented position; and conducting a phase pitexposure for exposing the original medium with a phase pit exposure beamwhich is slightly displaced in a radial direction from the track-centeroriented position, wherein a light amount of the phase pit exposure beamis reduced from a light amount of the groove exposure beam, wherein, inthe optical information recording medium, grooves serve as informationrecording tracks and phase pits are formed as preformatted informationon the tracks in a way such that radially opposite edge portions of thephase pits orthogonal to the tracks have tilt angles different from eachother, and wherein a center of the phase pits is radially displacedrelative to a track center of the grooves, a gap width of the phase pitsis greater than a gap width of the grooves such that each of the phasepits leaves a radial clearance from an immediately adjacent one of thegrooves, and gap depths of the grooves and the phase pits aresubstantially identical.
 10. An exposure method for exposing a masterfor manufacturing an optical information recording medium, said methodcomprising the steps of: exposing a light-sensitive layer of the master,to form on the light-sensitive layer a first latent image correspondingto a groove, by applying an exposure beam having constant lightintensity and centered at a center of a track on the master; andshifting the exposure beam in a radial direction from the center of thetrack, and exposing the light-sensitive layer with the shifted exposurebeam, to form on the light-sensitive layer a second latent imagecorresponding to a phase pit.
 11. A stamper manufacturing methodcomprising: forming a glass master including a light-sensitive layer;exposing the glass master including the light-sensitive layer byapplying the exposure method of claim 10; developing the light-sensitivelayer to form a groove pattern on the glass master; forming anelectrically conductive film on a surface of the glass master having thegroove pattern thereon; applying an electroforming process to form astamper plate on the conductive film; and peeling the stamper plate fromthe glass master, and processing the stamper plate to form a stamper.12. A stamper formed by the stamper manufacturing method of claim 11.13. An optical information recording medium manufacturing methodincluding the exposure method of claim
 10. 14. An optical informationrecording medium manufactured by the optical information recordingmedium manufacturing method of claim
 13. 15. An optical informationrecording medium master manufacturing apparatus comprising: a laserlight source; and a laser control unit, wherein said laser control unitcontrols said laser light source to apply an exposure beam to a master,in accordance with the exposure method of claim
 10. 16. A stampermanufacturing apparatus including the master manufacturing apparatus ofclaim 15.